1. Field of the Invention
The invention relates to a micro-machine mems switch, with electrical insulator and more particularly to a micro-machine switch used for opening and closing an electric contact.
2. Description of the Related Art
As one of conventional micro-machine switches, the micro-machine switch suggested in Japanese Unexamined Patent Publication No. 9-17300, which is based on the U.S. patent application Ser. No. 08/493,445 filed on Jun. 22, 1995 and assigned to Rockwell International Corporation, is illustrated in FIGS. 1A and 1B. FIG. 1A is a plan view of the same, and FIG. 1B is a cross-sectional view taken along the line 1Bxe2x80x941B in FIG. 1A.
An anchor 114 composed of thermosetting polyimide, a lower electrode 116 composed of gold, and a signal line 118 composed of gold are formed on a substrate 112 composed of GaAs.
A cantilever arm 120 supported at one end on the anchor 114 extends beyond the lower electrode 116 and to the signal line 118, and faces both the lower electrode 116 and the signal line 118 with a spatial gap therebetween. The cantilever arm 120 is comprised of silicon dioxide films.
An upper electrode 124 composed of aluminum is formed on the cantilever arm 120, extending from the anchor 114 to the lower electrode 116.
A contact electrode 122 composed of gold is formed on a lower surface of the cantilever arm 120 in alignment with the signal line 118.
The signal line 118 faces the contact electrode 122 with a gap therebetween. Accordingly, when no voltage is applied to the micro-machine switch, no current runs through the signal line 118.
On application of a voltage of 30V across the upper electrode 124 and the lower electrode 116, there is generated electrostatic force which pulls the upper electrode 124 towards the substrate 112. Hence, the cantilever arm 120 is downwardly deformed, resulting in that the contact electrode 122 makes contact with the signal line 118, and accordingly, a current runs through the signal line 118.
Thus, it is possible to make a current run through the signal line 118 or stop a current from doing the same by applying a voltage across the upper electrode 124 and the lower electrode 116 or stopping application of the voltage.
However, the conventional micro-machine switch 110 illustrated in FIGS. 1A and 1B is accompanied with the following problems.
When the cantilever arm 120 is deformed towards the substrate 112, the contact electrode 122 located at a distal end of the cantilever 120 first makes contact with the signal line 118, and then, the upper electrode 124 is attracted towards the lower electrode 116. In this situation, a force is applied to the cantilever arm 120 at a proximal end, and not at a distal end of the cantilever arm 120.
As a result, the contact electrode 122 does not make parallel contact with the signal line 118, but makes contact with the signal line 118 at a certain angle. That is, the contact electrode 122 makes contact with the signal line 118 only in a certain area. This causes non-uniformity in a contact resistance of the signal line 118, and degrades an area at which the contact electrode 122 makes contact with the signal line 118, in a lifetime test in which a load is applied to the signal line 118.
That is, the first problem is remarkable deterioration in contact performance.
In the micro-machine switch 110 having a structure where a force is applied to the cantilever arm 120 at a proximal end thereof to thereby cause the contact electrode 122 to make contact with the signal line 118, it is considered that the contact electrode 122 slides relative to the signal line 118. The slide movement between the contact electrode 122 and the signal line 118 increases an adhesive force generated therebetween in dependence on materials of which the contact electrode 122 and the signal line 118 are composed and a contact force therebetween, resulting in problems of non-uniformity in a restoring voltage and troubles in operation.
In the micro-machine switch 110, the contact electrode 122 and the signal line 118 are both composed of gold. Since gold has high electrical conductivity, it would be possible for a switch composed of gold to accomplish small insertion loss and high current-running capacity. However, since gold has a highest adhesion coefficient, gold would generate a high adhesive force.
An operational voltage at which the micro-machine switch 110 operates is dependent on a restoring force generated by the cantilever arm 120 and an electrostatic force generated between the upper electrode 124 and the lower electrode 116.
On the other hand, a characteristic of a contact resistance between the signal line 118 and the upper electrode 122 is dependent predominantly of a contact force. One of factors for determining a contact force is a spring constant of the cantilever 120 after the contact electrode has made contact with the signal line 118.
That is, stiffness of the cantilever arm 120 determines a characteristic of an operational voltage and a characteristic of a contact resistance. Hence, the micro-machine switch 110 has to be designed taking a balance between those characteristics into consideration, resulting in reduction in designability of the micro-machine switch 110.
The conventional micro-switch 110 is singly fabricated on the single substrate 112, and controls on/off of the signal line 118. In other words, the conventional micro-machine switch 110 has only one signal-input section and only one signal-output section. Hence, if a signal was to be output into a predetermined signal line among a plurality of signal lines, it was necessary to fabricate a circuit including a plurality of the micro-machine switches 110 each formed on the substrate 112.
However, such a circuit would increase a size of a system board including the circuit, and further increase a cost of fabricating the system board.
Japanese Unexamined Patent Publication No. 9-147720 has suggested a relay unit including a movable contact block having a movable contact at a center in an upper surface thereof and further having a movable piece deformable in a thickness-wise direction in accordance with an external signal, and a fixed contact block having a fixed contact facing the movable contact, the fixed contact being capable of making contact with and separating away from the movable contact.
Japanese Unexamined Patent Publication No. 9-269336 has suggested a micro G switch including a beam and a movable mass both fabricated by processing a silicon substrate. The movable mass is comprised of a movable contact supported by the beam, and a fixed contact formed on a glass substrate in facing relation to the movable contact. A center of gravity of the movable mass is located on a center line of the beam. The beam, the movable mass, the movable contact and the fixed contact are positioned in a hermetically sealed space formed by the silicon and glass substrates.
The above-mentioned problems remain unsolved even in the above-mentioned Publications.
In view of the above-mentioned problems in the conventional micro-machine switches, it is an object of the present invention to provide a micro-machine switch which is capable of stably operating and being fabricated in low costs.
In one aspect of the present invention, there is provided a micro-machine switch which causes a contact electrode to make contact with or separate away from a signal line formed on a substrate, to thereby turn on or off the signal line, including (a) first to N-th lower electrodes formed on the substrate, wherein N is an integer equal to or greater than 2, (b) first to N-th upper electrodes supported facing the first to N-th lower electrodes, respectively, and (c) a device for vertically raising and lowering the first to N-th upper electrodes between a first position where the contact electrode makes contact with the signal line when electrostatic force is generated between the first to N-th upper electrodes and the first to N-th lower electrodes, respectively, and a second position where the contact electrode is separated away from the signal line when the electrostatic force is not generated.
It is preferable that the first to N-th lower electrodes are located in symmetry about the signal line.
It is preferable that the first to N-th upper electrodes are located in symmetry about the contact electrode.
There is further provided a micro-machine switch which causes a contact electrode to make contact with or separate away from a signal line formed on a substrate, to thereby turn on or off the signal line, including (a) a first support formed on the substrate, (b) a second support formed on the substrate at a distance away from the first support, (c) a first upper electrode located between the first and second supports, (d) a second upper electrode located between the first upper electrode and the second support, (e) a first resilient member connecting the first support and the first upper electrode to each other such that the first upper electrode is kept floating above the substrate, (f) a second resilient member connecting the second support and the second upper electrode to each other such that the second upper electrode is kept floating above the substrate, (g) a first lower electrode formed on the substrate below the first upper electrode, and (h) a second lower electrode formed on the substrate below the second upper electrode, the contact electrode being supported between the first and second upper electrodes such that the contact electrode is floating above the substrate, the contact electrode being caused to make contact with the signal line when electrostatic force is generated between the first upper electrode and the first lower electrode and further between the second upper electrode and the second lower electrode, the contact electrode being separated away from the signal line due to restoring force generated by the first and second resilient members.
In the above-mentioned micro-machine switch, the first support, the first resilient member, the first upper electrode, the contact electrode, the second upper electrode, the second resilient member and the second support are arranged in this order. The first resilient member, the first upper electrode, the contact electrode, the second upper electrode and the second resilient member are supported floating above the substrate. On the substrate are formed the first and second lower electrodes facing the first and second upper electrodes, respectively.
By applying a voltage between the first and second upper electrodes and the first and second lower electrodes, there is generated an electrostatic force. By increasing this voltage, the generated electrostatic force increases, and hence, the first and second upper electrodes are attracted to the first and second lower electrodes, and resultingly, the contact electrode approaches the signal line.
By further increasing the voltage, a restoring force caused by the first and second resilient members overcomes the electrostatic force, and accordingly, the contact electrode makes contact with the signal line. Thus, the signal line is turned on.
By decreasing the voltage, the contact electrode separates away from the signal line due to the restoring force of the first and second resilient members. As a result, the signal line is turned off.
In the conventional micro-machine switch illustrated in FIGS. 1A and 1B, since the contact electrode moved in a curved line and then made contact with the signal line, there were caused problems of partial contact between the contact electrode and the signal line and slide movement of the contact electrode relative to the signal line.
In contrast, the contact electrode in the present invention makes contact with or separates away from the signal line with being positioned between the first and second upper electrodes. Thus, the contact electrode in the present invention moves in parallel with the signal line when making contact with the signal line, ensuring that the above-mentioned problems of partial contact and slide movement are no longer caused.
The micro-machine switch in accordance with the present invention may have the following structure and function.
The micro-machine switch electrically connects a first signal line formed on a substrate, to a second signal line spaced away from one end of the first signal line, or electrically disconnects the first signal line from the second signal line.
The micro-machine switch includes first and second supports fixed on the substrate and positioned in the vicinity of a space between the first and second signal lines and in symmetry about the signal line, first and second resilient members projecting from the first and second supports, respectively, and mechanically and electrically connected to the first and second supports, respectively, first and second upper electrodes mechanically and electrically connected to the first and second resilient members, respectively, an electrically insulating plate fixed to lower surfaces of the first and second upper electrodes and horizontally spaced away from the substrate, first and second lower electrodes formed on the substrate in alignment with the first and second upper electrodes, respectively, and a contact electrode mounted on a lower surface of the electrically insulating plate.
The first support, the first resilient member and the first upper electrode all located at a side of the signal line are integrally formed, and the second support, the second resilient member and the second upper electrode all located at the other side of the signal line are integrally formed. The contact electrode is equally spaced away from the first and second upper electrodes.
By applying a voltage across the first and second upper electrodes and the first and second lower electrodes, electrostatic forces having the same intensity are generated at the opposite sides of the contact electrode. The electrostatic forces allow the contact electrode to make contact with the signal line in parallel. When the voltage is stopped from being applied across the first and second upper electrodes and the first and second lower electrodes, the contact electrode separates away from the signal line in parallel.
Thus, it is possible to solve the above-mentioned problems of partial contact and slide movement, and ensure a preferred characteristic in operation.
By composing the contact electrode of ruthenium, for instance, it would be possible to reduce an adhesive force of the contact electrode down to such a degree that the adhesive force does not harmfully influence an operational characteristic of the micro-machine switch.
In the micro-machine switch in accordance with the present invention, after the contact electrode has made contact with the signal line, the electrical insulating member surrounds the contact electrode. As a result, a contact force which determines a contact resistance characteristic can be ensured due to stiffness of the electrical insulating plate, and has nothing to do with stiffness of the first and second resilient members which determine an operational voltage characteristic.
Hence, the designability of the micro-machine switch can be enhanced.
A plurality of the above-mentioned micro-machine switches may be formed on a single substrate. Specifically, a plurality of signal input sections and a plurality of signal output sections are formed on a single substrate, and the micro-machine switches are arranged across the signal input sections and the signal output sections. This arrangement makes it possible to output a signal into a predetermined signal output section. This ensures reduction in a size of a system board including the micro-machine switches.
It is preferable that the micro-machine switch further includes an electrical insulator extending between the first and second resilient members in parallel with the substrate, and having a first surface facing the substrate and a second surface not facing the substrate, the contact electrode being mounted on the first surface of the electrical insulator, the first and second upper electrodes being mounted on the second surface of the electrical insulator.
For instance, the electrical insulator may be in the form of a plate.
It is preferable that the micro-machine switch further includes a first pad formed on the substrate and electrically connected to the first upper electrode through a wire, and a second pad formed on the substrate and electrically connected to the second upper electrode through a wire.
It is preferable that the micro-machine switch further includes a third pad formed on the substrate and electrically connected to the first lower electrode through a wire, and a fourth pad formed on the substrate and electrically connected to the second lower electrode through a wire.
It is preferable that the substrate has a grounded area surrounding the signal line, the grounded area being electrically connected to the first and second lower electrodes.
It is preferable that the grounded area surrounds the signal line at a constant distance therebetween.
For instance, the substrate may be composed of glass or silicon.
It is preferable that at least a surface of the contact electrode is composed of ruthenium (Ru), rhodium (Rh) or gold cobalt, in which case, it is preferable that the contact electrode is composed of gold except the surface.
It is preferable that at least a surface of the signal line is composed of ruthenium (Ru), rhodium (Rh) or gold cobalt, in which case, it is preferable that the signal line is composed of gold except the surface.
The micro-machine switch may further include a reinforcing plate mounted on the second surface of the electrical insulator between the first and second upper electrodes.
It is preferable that the reinforcing plate has a larger area than an area of the contact electrode, and has a greater thickness than thicknesses of the contact electrode and the electrical insulator.
It is preferable that a first gap between the first upper electrode and the first lower electrode is equal to a second gap between the second upper electrode and the second lower electrode, and the first and second gaps are greater than a third gap between the contact electrode and the signal line.
It is preferable that the first and second upper electrodes are electrically connected to each other through a wire, and the first and second lower electrodes are electrically connected to each other through a wire.
In another aspect of the present invention, there is provided a micro-machine switch unit including (a) a substrate, (b) first to N-th micro-machine switches wherein N is an integer equal to or greater than 2, and (c) a common signal line and first to N-th signal lines all formed on the substrate, a K-th micro-machine switch electrically connecting the common signal line to a K-th signal line and electrically disconnecting the common signal line from a K-th signal line wherein K is an integer in the range of 1 to N both inclusive. Each of the first to N-th micro-machine switches is comprised of the above-mentioned micro-machine switch.
In still another aspect of the present invention, there is provided a method of fabricating a micro-machine switch including a first substrate, first and second supports standing on the first substrate, first and second upper electrodes located between the first and second supports, and first and second resilient members connecting the first and second supports to the first and second upper electrodes such that the first and second upper electrodes are kept floating above the first substrate, the method including the steps of (a) etching the first substrate in a selected area, (b) forming a mask on the first substrate, (c) diffusing an impurity into the first substrate in an area not covered with the mask, to thereby make a pattern of the first and second supports, the first and second upper electrodes, and the first and second resilient members, (d) forming an electrical insulator on the first substrate such that the first and second upper electrodes are located on the electrical insulator, (e) forming a contact electrode between the first and second upper electrodes, (f) fixating the first substrate on a second substrate such that the first and second supports stand on the second substrate, a signal line being formed on the second substrate in alignment with the contact electrode, first and second lower electrodes being formed on the second substrate in alignment with the first and second upper electrodes, respectively, and (g) melting the first substrate except the area into which the impurity was diffused.
It is preferable that a pattern of a reinforcing plate is also made in the step (c), the reinforcing plate being mounted on the electrical conductor between the first and second upper electrodes in a final product.
It is preferable that the first substrate is fixated to the second substrate in the step (f) by electrostatic bonding.
It is preferable that the first substrate is composed of silicon and the second substrate is composed of ceramics or GaAs, and the first substrate is fixated to the second substrate through an adhesive.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
In accordance with the present invention, a contact electrode moves in parallel with a signal line, and makes contact with the signal line. Thus, the problems of partial contact between a contact electrode and a signal line and slide movement between a contact electrode and a signal line, which remain unsolved in the conventional micro-machine switch, can be solved. Accordingly, the micro-machine switch can stable operate.
In other words, in the micro-machine switch in accordance with the present invention, electrostatic forces necessary for turning a signal line on are generated in symmetry about a contact electrode, and restoring forces necessary for turning a signal line off are generated in symmetry about a contact electrode. This structure enables a contact electrode to make contact with a signal line almost in parallel. Hence, it would be possible to prevent partial contact and slide movement of a contact electrode when the contact electrode makes contact with or separates away from a signal line.
In addition, by composing a contact electrode of rhodium, ruthenium or gold cobalt, it would be possible to minimize adhesion in a contact area of a contact electrode at which the contact electrode makes contact with a signal line, ensuring both reduction in non-uniformity in a voltage to be applied across the upper and lower electrodes, and prevention of troubles in operation.
An operational voltage can be ensured by stiffness of the first and second resilient members, and a contact force of a contact area where a contact electrode makes contact with a signal line can be ensured by stiffness of the electrical insulator. As a result, the micro-machine switch could have enhanced designability.
Furthermore, a plurality of output signal lines, a common signal line electrically connected to each of the output signal lines, and a plurality of the micromachine switches can be formed on a single substrate. This ensures that an apparatus which can turn on or off a plurality of signal lines can be fabricated in a small size and in low fabrication costs.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.